The present invention relates to a lubricating apparatus for four-cycle engines, and more particularly to a lubricating apparatus for small-sized four-cycle engines to be used in portable type bush cutters, knapsack type powered sprayers, and the like which take a slanted position as one of their work postures.
Generally, engines used as the power units of such machines as portable type cutters (trimmers) for plants and knapsack type powered sprayers to be carried by hand or on operator's back in operation require operational stability even in the cases where the machines are slanted in use.
Among various types of engines, two-cycle engines comprise a mechanism for carrying out the lubrication of moving parts by inhaling lubricating oil and fuel into the inside of the engines by means of negative pressures created in rising pistons; therefore, construction being capable of free-angle use can be easily obtained therefrom. On this account, two-cycle engines are widely used for the above-mentioned portable type machines.
Meanwhile, four-cycle engines also as another type of engines can be made into small-sized and light-weighted ones due to progress in design and manufacturing technology. However, on account of adopting such construction that the oil sump (oil pan) as a component part of the lubricating apparatus is arranged under a crank room and oil is splashed up or pumped up from the oil sump to lubricate moving parts, four-cycle engines are supposed to be used basically in an upright state. In other words, four-cycle engines are inferior to two-cycle ones in lubricating mechanisms.
However, two-cycle engines in turn have problems in higher content of hydrocarbon in their exhaust gas and louder noise. Accordingly, in terms of exhaust gas clean-up and prevention of working-environment deterioration, it has been desired in recent years to use four-cycle engines being favorable in exhaust gas property and low in noise for the portable machines.
In view of the foregoing, the applicant of the present invention has previously proposed a lubricating apparatus for four-cycle engines which utilizes the phenomenon that the pressure in a crank room varies in accordance with the piston's up-and-down movements (e.g., Japanese Patent Application Laid-Open No. Hei 10-288019).
In the proposition, with the oil sump and the crank room completely shut off from each other, an intermittent oil feeding means is to be arranged from the oil sump to a portion in the rotational track of a crankshaft to provide communication between the oil sump and the crank room so that oil is inhaled from the oil sump and fed into the crank room by means of a negative pressure in the crank room. Besides, the crank room is to be further communicated with a valve gear room equipped with cam mechanisms and the installation place of valve drive mechanisms to forcedly send oil mist agitated in the crank room under a positive pressure generated inside the crank room in the descending of the piston.
In the meantime, blowby gas containing the oil mist fed into the valve gear room is to be recovered into the oil sump by means of a negative-pressurization tendency of the oil sump, in other words, by the action of the negative pressure inside the crank room created in the ascending of the piston upon the oil sump.
Including such constitution, however, the pressure in the oil sump increases with a rise in cylinder temperature once engine is started. On account of this, the attempt to recover the oil from the valve gear room into the oil sump sometimes ends up in poor recovery since sufficient negative pressures cannot be obtained inside the oil sump. This excessively retains the oil inside the valve gear room, causing the danger of a lack in lubricating oil for other parts.
In addition to the case of being used under such conditions that the piston in its combustion chamber is reciprocated mostly in a vertical direction, in other words, the crankshaft as an output shaft of power is directed horizontally, a four-cycle engine having constitution described in the aforesaid publication is sometimes used under such conditions that the crankshaft is mostly directed in a vertical direction. The latter use conditions include applications such as a lawn mower.
In the cases where the crankshaft is vertically directed, in other words, the cases of vertical type use, the engine takes a so-called sideways position in which its recoil starter is directed up and the reciprocation direction of the piston becomes horizontal. Here, in the valve gear room into which the oil is collected, the opening of an oil returning channel provided to return the oil component of the oil mist into the oil sump gets out of the oil surface, possibly hampering the smooth returning of oil. Besides, in the cases where a slidably supported portion of a valve is left immersed in the oil, the oil penetrates into the combustion chamber via the slidably supported portion, possibly causing the adverse effects of defective combustion such as white smoke emission and of sticking carbon to the muffler.